1. Field of the Invention
The present invention relates to an image synthesizing system which can perform the synthesization of high-quality image in real time.
2. Description of the Related Art
There are known various image synthesizing systems used as in three-dimensional (3-D) games, airplane or other vehicle simulators and so on. Typically, such image synthesizing systems have information of image relating to a 3-D object 300 as shown in FIG. 10, which has previously been stored therein. Information of image is perspective transformed into a pseudo 3-D image 308 on a screen 806. As a player 302 makes an operation with a control panel 304 such as rotation, translation or the like, the system responds to the control signal to perform the processing with respect to rotation, translation or the like of the image of the 3-D object 300 in real time. Thereafter, the processed 3-D image is perspective transformed into the pseudo 3-D image on the screen 306. As a result, the player 302 itself can rotate or translate the three-dimensional objects in real time to experience a virtual 3-D space.
FIG. 11 shows one of such image synthesizing systems. The image synthesizing system will be described as being applied to a 3-D game.
As shown in FIG. 11, the image synthesizing system comprises an operator's control unit 510, a game space processing unit 500, an image synthesizing unit 512 and a CRT 518.
The game space processing unit 500 sets a game space in response to control signals from the operator's control unit 510 and in accordance with a game program which has been stored in a central processing unit 506. Namely, the processing is performed with respect to what position End direction the 3-D object 300 should be arranged in.
The image synthesizing unit 512 comprises an image supply unit 514 and an image forming unit 516. The image synthesizing unit 512 performs the synthesization of a pseudo 3-D image in accordance with information of a game space set by the game space processing unit 500.
In this image synthesizing system, 3-D objects in the game space are defined as polyhedron which are divided into 3-D polygons. As shown in FIG. 12, for example, the 3-D object 300 is represented as a polyhedron which is divided into 3-D polygons 1-6 (polygons 4-6 not shown herein). The coordinates and associated data of each vertex in each of the 3-D polygons (which will be referred to "image data of vertices") have been stored in a 3-D image data storage unit 552.
The image supply unit 514 performs various mathmatical treatments such as rotation, translation and others, and various coordinate conversions such as perspective transformation and others, on the image data of vertices, in accordance with the setting of the game space processing unit 500. After the image data of vertices has been processed, it is permuted in a given order before outputted to the image forming unit 516.
The image forming unit 516 comprises a polygon generator 570 and a palette circuit 580. The polygon generator 570 comprises an outline point processing unit 324 and a line processor 326. The image forming unit 516 is adapted to perform a process of painting all the dots (pixels) in the polygon with a predetermined color data or the like in the following procedure:
First of all, the outline point processing unit 324 calculates left-hand and right-hand outline points which are intersection points between polygon edges AB, BC, CD, DA and other polygon edges and scan lines. Subsequently, the line processor 326 paints, with specified color data, sections between the left-hand and right-hand outline points, for example, sections between L and Q; Q and R as shown in FIG. 12. In FIG. 12, the section between L and Q is painted by red color data while the section between Q and R is painted by blue color data. Thereafter, the color data used on painting are transformed into RGB data in the palette circuit 580, and then the RGB data in turn is outputted to and displayed in CRT 518.
When such a painting is to be carried out and if a plurality of polygons are overlapped with one another, it is required that only the parts of the'polygons which are not overlapped by polygons closer to the view point. For this purpose, the image synthesizing system of the prior art uses a technique of sequentially painting the polygons, starting from the remotest polygon on from the view point on the screen.
However, such a type of image synthesizing systems are usually required to perform the real-time image processing. More particularly, they are required to update image data contained in one scene (in some cases, two scenes) per one field, for example, per 1/60 seconds. Therefore, the image synthesizing systems must treat the image at high speed, which would otherwise reduce the quality of image. The efficiency of the high-speed image processing most depends on the painting step wherein all the dots in the image are painted with the predetermined colors.
In the prior art, the polygons are sequentially painted starting from a polygon remotest from the view point in the screen. Therefore, entire area of the polygons appearing in one field including overlapped parts must be painted through the most time consuming painting step. Any polygon part hidden by the overlap between the polygons will never be represented on the screen. The prior art will unnecessarily treat such a hidden polygon part. This will provide an unsatisfactory technique of processing the image in real time.
When it is required to paint the polygons starting from the remotest polygon from the view point in the scene and if an increased number of polygons could not be painted within one field, the data relating to these polygons will be lost starting from that of the closest polygon to the view point in the scene. However, the closest polygon to the view point is usually one that is most observed by the player and most important in the game. The loss of such important polygons are not desirable in maintaining the quality of scene higher.